Dentists and oral surgeons typically utilize x-ray apparatus to examine patients prior to treatment. Film placed in the patient's mouth is exposed to the x-rays which pass through the soft tissue of skin and gums and are absorbed or refracted by the harder bone and teeth structures. The film is then chemically developed and dried to produce the image from which the dentist makes appropriate treatment; evaluations. Such technology, though with many refinements, has not basically changed over the past fifty years.
Though the technology is a mature one and well understood in the field, there are numerous drawbacks in conventional dental radiology which utilizes film for image capturing. Foremost among such problems is the radiation dosage, which optimally for conventional film exposure, is about 260 millirads. Since the high energy electrons from x-ray sources can cause damage to the nuclei of cells it is agreed that minimizing radiation exposure is highly desirable. In this regard, the average dose for dental x-rays has been reduced by 50% over the last thirty years, to the current levels, mostly as a result of improvement in film sensitivity. Further incremental reductions in requisite x-ray dosage for film exposure is unlikely to be of any great extent.
Film processing itself presents other problems including the time, expense, inconvenience and uncertainty of processing x-ray films and many times the exposure is defective or blurred. The minimum time for development is four to six minutes. In addition, there is the cost and inconvenience of storing and disposing of the developing chemicals which are usually environmentally harmful.
To obviate these problems, various expedients have been proposed or developed for the purpose of x-ray imaging without film. The general principal in all of such expedients has been the conversion of x-ray radiation into visible light by scintillators and conversion of the light into electrical video signals for viewing or into electrical signals for printing. Representative of such expedients are U.S. Pat. No. 4,160,997, issued to Robert Schwartz; U.S. Pat. No. 4,593,400, issued to Francis Mouyen; and U.S. Pat. No. 4,987,307, issued to Giorgio Rizzo and Cesare Gadda. All of such patents, and others in the field, embodied sensors which included phosphor scintillator screens and separated and distinct CCD elements for conversion of light to electrical signals. The CCD elements, because of limitations in capability and sensitivity to hard x-rays, required additional light processing enhancing and x-ray shielding components in the sensor. Examples of such additional components include the pyramidal optical fiber containing screen of Mouyen, specifically used to obviate problems with the Schwartz sensor, and the micro-lens system of Rizzo et al., specifically described as obviating problems with optical fiber containing sensors.
As a result of the various "improvements" the sensors of the prior art were relatively bulky compared to dental x-ray film. Mouyen, for example, describes his sensor as being up to 17 mm thick. This presents problems in proper oral placement and manipulation in adult patients and severely restricts pediatric use.
Furthermore, the additional components entail greater costs, introduce problems with component degradation and failure, and generally preclude direct sterilization by dental autoclaving. The sensors of the prior art are accordingly usually described as being used with disposable plastic sleeves. However, such sleeves while useful, may be occasionally susceptible to perforation during use, a dangerous situation with prevalent communicable diseases.
Finally, the systems described provided resolution of images substantially below that of x-ray dental film. Thus, though x-ray dosage is reduced, it is at the cost of diagnostic accuracy.